Known shift-by-wire automatic transmissions generally assume a park mode by default in the event of an electrical power failure such as a flat battery or other fault, for example due to a collision. Recovery of the vehicle can therefore be difficult due to locking of the wheels of the vehicle by the transmission.
When the transmission is in the park mode one or more wheels of the vehicle may be locked by the transmission. If the park mode is deselected the one or more wheels are released, allowing the one or more wheels to freely rotate. The state of the transmission may be controlled by means of a rotatable selector shaft, different transmission modes corresponding to different respective rotational positions of the selector shaft.
In some known arrangements a latching release lever is provided behind a dashboard trim panel in a cabin of the vehicle. The release lever is coupled by means of a Bowden cable arrangement to a selector shaft lever that is fixed to the selector shaft. The transmission may be released from the park mode by rotating the latching release lever through a required angle to a latch position, in which the lever remains until it is unlatched. As the lever is rotated, the Bowden cable causes the selector shaft lever to rotate from a transmission park mode position to a transmission park released state position, thereby releasing the transmission from the park mode.
It is to be understood that the transmission selector shaft is typically spring loaded such that if the shaft is released the shaft rotates automatically under the bias of a spring member of the transmission to the park mode position.
In another known arrangement a threaded bracket is mounted adjacent the selector shaft lever at a location such that it does not interfere with required movement of the selector shaft lever in normal operation. When it is required to release the transmission from the park state, a bolt is screwed through the bracket until it abuts the lever. Continued rotation of the bolt causes deflection of the selector shaft lever. The bolt may be screwed through the bracket until the selector shaft lever has been rotated to the park release position.
A disadvantage of this arrangement is that a person manipulating the bolt is required to crawl underneath a vehicle to be moved in order to access the bolt. If the vehicle moves unexpectedly when the bolt is manipulated, the person under the vehicle may be injured. Furthermore, to arrest movement of the vehicle the person manipulating the bolt must unscrew the bolt quickly to allow the transmission to resume the park mode. In practical situations there may not be sufficient time to unscrew the bolt before injury occurs.
It is also known to provide a vehicle having an electric park brake. The park brake is deployed or released by rotation of a shaft such as a selector shaft or actuation shaft by means of an electric motor or hydraulic fluid pressure under the control of an electrical controller. If a vehicle suffers electrical failure when the park brake is deployed the vehicle may become immobilised due to inability to rotate the shaft. In embodiments having a shaft actuated by hydraulic fluid pressure the vehicle may become immobilised if either electrical power or hydraulic fluid pressure is not available.
It is against this background that the present invention has been conceived. Embodiments of the invention may provide an arrangement or a method which addresses one or more of the above problems. Other aims and advantages of the invention will become apparent from the following description, claims and drawings.